Abstract

A study was conducted to assess soil erosion using Geographical Information System
(GIS) and Universal Soil Loss Equations (USLE) for the Sg. Hijau watershed. The study
area, located in Fraser's Hill, Pahang is 1.5 km2 in size and lies between 1060 and 1350
m a.s.l. A GIS software, ARC/INFO version 3.4 was used to develop the database.
Analysis was carried out using the ArcView Spatial Analyst Version 1.1 and ArcView
3D Analyst. Results obtained show that about 48% of the Sg. Hijau catchment falls under
the slope gradient of 12°_25° while 26% of the area under the slope of more than 25°.
Four empirical methods based on the applications of erosivity were used for soil erosion
computation. They were from Roose (1975), Balamurugan (1990), Morgan (1974) and
rainfall of more than 25 mm/hr adopted in this study. By comparison, Roose generated
the highest erosion rate with 1.757 t/ha/yr followed by Balamurugan with 0.685 t/ha/yr,
25 mm/hr with 0.567 t/ha/yr and lastly, Morgan with 0.532 t/ha/yr. Erosion rates of less
than 1 t/ha/yr were computed for most of the area in the study watershed: soil erosion
rates ranged from 0.363 to 0.642 t/ha/yr. The results obtained were also comparable to
measured soil loss from erosion plots in other studies under similar conditions. Most
studies have shown that erosion seldom exceeds 1 t/ha/yr under forest conditions. This
study showed that soil erosion rates could be calculated using USLE within the GIS
environment. Apart from employing GIS as an easy-to-use database and toolkit for
modeling, GIS techniques could be used to assess the uncertainty and validity of spatial
erosion models. The use in catchment hydrological and erosion modeling offers
considerable potential.